The regulation of LH/hCG receptors in testis and ovary has been analyzed with particular reference to the control of receptor concentration by changes in the homologous hormone. Both LH and hCG were found to cause marked decreases in receptors of testis and ovary, with consequent densitization of adenylate cyclase and steroidogenic responses to gonadotrophic hormones. These studies have indicated that hormone-receptor loss, by a mechanism that appears to involve turnover or processing of the hormone-receptor complex. These processes were investigated in Leydig cells and ovarian luteal cells to determine the effects of hormone-induced receptor regulation on the responsiveness of the endocrine target cells.